Journal
MOLECULAR MEMBRANE BIOLOGY
Volume 26, Issue 3, Pages 194-204Publisher
TAYLOR & FRANCIS LTD
DOI: 10.1080/09687680902733815
Keywords
Lipid flip-flop; transmembrane asymmetry; cholesterol; ceramide; dihydroceramide; sphingolipids; liquid ordered phase; spin-labels
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Funding
- Centre National de la Recherche Scientifique [UMR 7099]
- European Union [HPRNCT-2000-0077, MRTN-CT2004-005330]
- COST
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In order to study the basic physical phenomena underlying complex lipid transbilayer movement in biological membranes, we have measured the transmembrane diffusion of spin-labelled analogues of sphingolipids in phosphatidylcholine (PC) large unilamellar vesicles in the absence or presence of cholesterol, going from a fluid (liquid disordered) l(d), phase to a more viscous, liquid ordered (l(o)), phase. We have found cholesterol to reduce the transverse diffusion of glucosylceramide (GlcCer) and galactosylceramide (GalCer) in a concentration-dependent manner. However, surprisingly, we could neither detect any influence of cholesterol on the rapid flip-flop of ceramide nor on the flip-flop of dihydroceramide, for which the tau(1/2) of flip-flop remains in the order of 1 minute at 20 degrees C in the presence of cholesterol. As a consequence of rapid flip-flop of ceramide in both the l(o) and the l(d) phase, ceramide is likely to distribute between the two monolayers of a membrane, and could in principle partition into segregated domains in each side of the plasma membrane of eukaryotic cells.
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